1. Field of the Invention
This invention relates to a pilot burner for use in connection with gas-fired heating equipment such as boilers and furnaces. More particularly, this invention relates to a pilot burner for the main burners utilized in such heating equipment having the capability of not only igniting the main burners, but also having the capability of controlling the fuel/air ratio at which such main burners are fired. The pilot burner of this invention is particularly suitable for use in connection with closed loop control of burners, having the capability of functioning both as a control burner in the closed loop control system as well as an ignition pilot.
2. Description of Prior Art
Modulated gas-fired heating equipment burners operate over a wide turndown range and most of these burners use a mechanical linkage to control the air/fuel ratio. The amount of excess air varies with burner turndown and is typically maintained at 15-20% excess air for high fire operation and increases to about 40% excess air for lower firing rates. These excess air levels are higher than those required for efficient combustion due to safety considerations. For mechanical linkage based fuel/air ratio control, there is typically a variation of plus or minus 1% in flue gas oxygen due to factors such as variation in air and gas properties as well as mechanical linkage hysteresis. Current closed loop air/fuel ratio control systems, based on O.sub.2 and CO measurements, are expensive and can only be justified for higher design firing rate burners.
Accordingly, there is a need for closed loop fuel/air ratio control systems which, in addition to being advantageously suitable for use at high firing rates, is also advantageously suitable for use at lower firing rates. There is also a need for closed loop fuel/air ratio control systems which eliminate the need for mechanical linkage fuel/air ratio control.
Multiple burner heating equipment applications present significant fuel/air ratio control problems because there is currently no easy way to control the fuel/air ratio of each burner. Thus, there is a need for a closed loop fuel/air ratio control system which enables each burner of a multiple burner application to be individually controlled.
Current closed loop fuel/air ratio control systems employ options such as O.sub.2 and CO analyzers for fuel/air ratio control. Such implementation generally tends to be relatively expensive. Thus, there is also a need for fuel/air ratio controllers for closed loop fuel/air ratio control systems which are lower in cost than such currently employed options.